In the area you fight him there is a yellow herb you can use with a green herb to increase your health. Grab it and use it to increase your health then let him kill you, which won't be that hard. After your game is over continue and you will have all of your green herbs again and the extra health. The yellow herb will be out there again so grab it and repeat the process increasing your health over and over again till its maxed out fairly early in the game.